The present invention relates to a wrench provided with an alternating current drive motor.
The state of the art encompasses pneumatic wrenches (air wrenches) which have a series of disadvantages. They require an expensive preparation of the air, relatively complicated devices for a constant maintaining of pressure and for an exact switching, and offer only a relatively lower torque in the rapid motion range.
Furthermore, wrenches are in use with alternating current drive motors, which are designed as single frequency asynchronous motors. These drive motors operate with at least two stage gears which, after the occurrence of a predetermined starting moment, switches over to a lower output speed of the wrench. Such wrenches are not useable for highly exact screwed joints since the exact stopping of the drive motor is difficult after reaching the predetermined starting moment at the higher rotation of speed of the motor. Furthermore, the energy required by such wrenches is relatively high.